Optimizing the fluoride removal using new carbons impregnated with a calcium solution extracted from egg shells

摘要

The excess of fluoride in drinking water is caused by natural or anthropogenic sources. Naturally in America, Africa and Asia, fluoride concentration in groundwater can be as high as 30 mg 1~(-1) and, according to the WHO, more than 260 million people world-wide consume drinking water with high fluoride concentrations. In Mexico, the states of San Luis Potosí, Durango, Aguascalientes, Zacatecas and Jalisco are especially affected by this problem. Nowadays, several techniques have been developed for treating fluoride-polluted waters, but, the adsorption method using activated carbon doped with specific compounds could be an efficient and economical alternative [1]. For this reason, the purpose of this study was to prepare low cost carbons from two common wastes in Mexico: pecan nut shells (Carya illinoinensis) that were used as carbon precursor and egg shell employed as a source of calcium solution. Specifically, modified carbons with calcium compounds were prepared following a Taguchi L_4 orthogonal array (see Table 1) and carbonizing at 800 °C using a tubular Carbolite furnace. The obtained samples were characterized and tested for fluoride removal. The combination of factors selected in the experiment 4 provides the better results in terms of fluoride removal with almost an efficiency of 84 % (see Table 1), in comparison with the sample obtained from pecan nut shell without impregnation with calcium solution (29%).